Riiiighttttt - - - Because manufacturers don't have any testing capability of their own, competitors would want to test on the same person's Jeep, and we all know there is nothing better than simply adding whatever random pieces come one's way is far better than building one's own Jeep to suit individual purpose.

As a heads-up, vendors sometimes choose testers by reading threads & carefully selecting a few folks that have been progressively building their Jeep. Some vendors have a selection process & a game plan to help ensure they receive quality feedback whether it be good, bad, or otherwise.

Sometimes vendors get screwed by folks after they get a free part or system. By that, I mean they disappear behind the woodshed & do not provide the vendor test results or adequate feedback. Basically they rip-off the vendor & don't hold up their end of the bargain. This has happened many times that I know of here on JF and on other forums.

As far as YJ's go, vendor testing & test candidates has become less & less over the last few years due to vendors looking to test newer models and products designed for newer Jeeps.

The list is long as far as me being asked to be a tester by vendors, so I have a little insight on the process.

Not sure that testing is the same in this world as in others.. but, from personal experience, just owning said device doesnt tend to get you into the development/testing phase of vendors. They usually look for testers who are "in the field" they are dealing with. Or they offer pro-deals where if you work for a company that sells their products, they will give you MASSIVE discounts on their new stuff... provided that you, by word of mouth, sell their product or give them feedback (depends on what they are looking to get back from you as an end-user.
Ive worked in several fields on both sides of that spectrum... pro-deals are easier to come by because there is a financial investment by the end user... and very few companies still actively use a third party "beta-tester" system.
It helps if you are already knowledgable of whatever equipment you are using and if you are well written and read by others.

Ok what about advertising for any venders. Maybe get a discount on there products?

This company has a photo contest going on right now.
You e mail them and get their sticker and a $25 in store credit.
Put the sticker on your Jeep and take a picture with the sticker in a place it can be seen and the Jeep in action.
Sumit the photo and if you are voted the best photo for the month you will win a $500 in store credit.http://steinjager.com/contest.php